| We studied two biological tissues with optically anisotropic structures: high moisture soy protein extrudates and skeletal muscles. High moisture extrusion has been used to produce vegetable meat analogs that resemble real animal meat and have significant health benefits. Since visual and textural properties are key factors for consumer acceptance, assessing fiber formation in the extruded soy protein product is important for quality control purpose. A non-destructive method based on photon migration was developed to measure fiber formation in extruded soy proteins. The measured fiber formation index in intact samples showed good agreement with that obtained from image analysis on peeled samples. By implementing this new method in a fast laser scanning system, we have acquired two dimensional mappings of fiber formation and orientation in the entire sample in real time.;In addition to fibrous structures, skeletal muscles have a unique periodic sarcomere structure which produces strong light diffractions. However, inconsistent experimental results have been reported in single fiber diffraction studies. By applying the three-dimensional coupled wave theory in a physical sarcomere model, we found that a variety of experimental observations can be explained if inhomogeneous muscle morphological profiles are considered. We also discovered that the sarcomere structure produced a unique optical reflectance pattern in whole muscle. None of the existing light propagation theories are able to describe this pattern. We developed a Monte Carlo model incorporating the sarcomere diffraction effect. The simulated results quantitatively resemble the unique patterns observed in experiments.;We used a set of parameters to quantify the optical reflectance profiles produced by a point incident light in whole muscle. Two parameters, q and B, were obtained by numerically fitting the equi-intensity contours of the reflectance pattern. Two spatial gradients were calculated along the directions parallel and perpendicular to muscle fibers. The mean diffuse intensity was obtained by excluding the specular reflectance. These five parameters provide a comprehensive and complete description of the diffuse reflectance in muscle. In a study of 336 muscle samples, we found these optical parameters were subject to the effects of different muscle physical and biochemical factors. Different types of muscle have significantly different diffuse intensities. Aging shows different effects on the q parameter in different muscles. In addition, the mean diffuse intensity is significantly different (p<0.05) in different animal breeds. Optical parameters showed good correlations with Warner-Bratzler shear force. Further studies on a large sample group are necessary to develop a statistical model to predict muscle physical and chemical properties using these non-destructive optical measurements. |
